Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$83.68	7.670%	$90.0983	$90.10	$90.10	$90.10
Purchase #2	$31.33	12.235%	$35.1632	$35.16	$35.15	$35.20
Purchase #3	$90.69	11.243%	$100.8863	$100.89	$100.90	$100.90
Purchase #4	$81.41	7.203%	$87.274	$87.27	$87.25	$87.30
Purchase #5	$183.76	10.534%	$203.1173	$203.12	$203.10	$203.10
Purchase #6	$216.75	10.503%	$239.5153	$239.52	$239.50	$239.50
Purchase #7	$144.95	5.134%	$152.3917	$152.39	$152.40	$152.40
7 purchase totals =	$832.57		$908.4461	$908.45	$908.40	$908.50